This invention relates to continuous inkjet printheads which integrate multiple nozzles on a single substrate and in which print nonprint operation is effected by controlled deflection of the ink as it leaves the printhead nozzle.
Many different types of digitally controlled printing systems have been invented, and many types are currently in production. These printing systems use a variety of actuation mechanisms, a variety of marking materials, and a variety of recording media. Examples of digital printing systems in current use include: laser electrophotographic printers; LED electrophotographic printers; dot matrix impact printers; thermal paper printers; film recorders; thermal wax printers; dye diffusion thermal transfer printers; and inkjet printers. However, at present, such electronic printing systems have not significantly replaced mechanical printing presses, even though this conventional method requires very expensive setup and is seldom commercially viable unless a few thousand copies of a particular page are to be printed. Thus, there is a need for improved digitally controlled printing systems, for example, being able to produce high quality color images at a high-speed and low cost, using standard paper.
Inkjet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing. Inkjet printing mechanisms can be categorized as either continuous inkjet or drop on demand inkjet. Continuous inkjet printing dates back to at least 1929. See U.S. Pat. No. 1,941,001 to Hansell.
U.S. Pat. No. 3,373,437, which issued to Sweet et al. in 1967, discloses an array of continuous inkjet nozzles wherein ink drops to be printed are selectively charged and deflected towards the recording medium. This technique is known as binary deflection continuous inkjet, and is used by several manufacturers, including Elmjet and Scitex.
U.S. Pat. No. 3,416,153, which issued to Hertz et al. in 1966, discloses a method of achieving variable optical density of printed spots in continuous inkjet printing using the electrostatic dispersion of a charged drop stream to modulate the number of droplets which pass through a small aperture. This technique is used in inkjet printers manufactured by Iris.
U.S. Pat. No. 3,878,519, which issued to Eaton in 1974, discloses a method and apparatus for synchronizing droplet formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates.
U.S. Pat. No. 4,346,387, which issued to Hertz in 1982 discloses a method and apparatus for controlling the electric charge on droplets formed by the breaking up of a pressurized liquid stream at a drop formation point located within the electric field having an electric potential gradient. Drop formation is effected at a point in the field corresponding to the desired predetermined charge to be placed on the droplets at the point of their formation. In addition to charging rings, deflection plates are used to deflect the drops.
Conventional continuous inkjet utilizes electrostatic charging rings that are placed close to the point where the drops are formed in a stream. In this manner individual drops may be charged. The charged drops may be deflected downstream by the presence of deflector plates that have a large potential difference between them. A gutter (sometimes referred to as a xe2x80x9ccatcherxe2x80x9d) may be used to intercept the charged drops, while the uncharged drops are free to strike the recording medium.
It is an object of the present invention to provide a high-speed continuous inkjet apparatus whereby drop deflection may occur at high repetition.
It is another object of the present invention to provide a high-speed continuous inkjet apparatus whereby drop formation and deflection may occur at high repetition.
These objects are achieved in an apparatus for controlling ink in a continuous inkjet printer in which a continuous stream of ink is emitted from a nozzle bore; the apparatus comprising:
a reservoir containing pressurized ink;
a rigid nozzle element defining an ink staging chamber and defining a nozzle bore in communication with the ink staging chamber arranged so as to establish a continuous flow of ink in a ink stream;
ink delivery means intermediate the reservoir and the ink staging chamber for communicating ink between the reservoir and defining first and second spaced ink delivery channels;
a first actuable flow delivery valve spaced from the nozzle bore and positioned in operative relationship with the first ink delivery channel and a second actuable flow delivery valve spaced from the nozzle bore positioned in operative relationship with the second ink delivery channel;
the first and second actuable flow delivery valves each including a flexible heat responsive element which when heated moves to a position that restricts flow in its corresponding ink delivery channel; and
means for selectively heating the first and second actuable flow delivery valves so that when both first and second actuable flow delivery valves are unheated ink is delivered through the nozzle along a first path and when the first actuable flow delivery valve is heated and the second actuable flow delivery valve is unheated, ink is delivered through the nozzle along a second path and when the second actuable flow delivery valve is heated and the first actuable flow delivery valve is unheated, ink is delivered through the nozzle along a third path wherein the first, second and third paths are spaced from each other.